Electric control circuit



Sept. 13, 1932,- o. T. FRANCIS 1,877,165

g ELECTRIC CONTROL CIRCUIT Filed Dec. 27, 1928 lnuen'or:

@liz/3er Y. Iiyancs,

Patented Sept. 13, 1932 i i UNITED [STA-Tes PATENT? [oFF-Ice .oLIvER n rRANoIs, orotmivcffrco,` vAIRGI'NIA l E'Lncrnrotoonrnonf entourerv Application aiedtnecemter 27,1923; Y Serial No, 328,662.

This invention relates to regulators of elecfading station by increasing the impedance of triccurrent and potential, and more particu- V3 Aduring the time that blasting ysignals larly to means for regulating the current and Would ordinarily occur, resulting in reducing potential derived from-'a varying source of the plater voltage impressed on the ampli `5 direct'cur're'nt, and still more particularly .to fiel' Vl. f- 1 regulating potentials impressed on the ele- To more' clearly illustrate the i'unctioningy ments of vacuum tube amplifiers and of the of'this circuit, let-us assume a specific exampotentials impressed on'the loads in the-outple. 'Assume Bl tobe180 volts, Nl to be put 'Circuits of amplifiers, Y K thel ordinary l neon lamp which starts function- 10 It is well known that crashes of static, local ingvvhen onehundredi and `forty volts is im- 60 disturbances and blasting signals from a fadpressed thereon andlrbecomes `rinoperative ing station causeV surges of current in the When the voltage impressed thereon drops to output circuit of electric amplifiers. Y one hundredg Assumethat Afour milliam- It is the Vobject of this invention to so conperes are flowing through the translating deis trol these surges that signals ofabove afprevice Si The negativefgridbias on V3 would y65 Y Y determined limit impressed on thev input Vcr- Vthen be'minus sixty eight volts as R2 is taken cuit shallbe eliminated entirely from the o utas seventeen lthousand ohms.' v'C2 may be four put circuit. Anotherobjectis to so regulate microfarads. To counteract thisexoessive the plate voltage impressed on the vacuum negative' fgrid bias'.v a C lbattery BZ of sixty@ 12b tube amplfierthat signals of `alcove the des ei ht volts hasbeen inserte'd in the grid cir? 7o sired strength such as those caused bya'blast- Cult' of this tube s'o that thev actual grid 'bias ing station shall befno louder than the weaker on the tube is zero'. y i l l Y signals received from sai'd'station. Bya referencelto Fig. 3,1 iind that When With these andother objects in View', the Eg is Zero and ourmilliamperes are Howinventionmay bemore readilyunderstood'by` ing'nthe' ClClltQthe IR drop through this 75 z treferencev to thev followingr description in element V3 wil-lbe Aof order of sixty-eight connection with the drawing which shows volts. Disregardi'ng the impedance ofthe diagrammatically several of the embodiments translating device at this time, the 4voltage impressed on Vl would therefore be 112 volts.

of the invention. v f

3B f Figure l shows a stage of amplification ein- Iffnow due-to the lblasting signal, the cur- 80 'i tioning of the* circuit.

ploying the circuitfbreakerVN- in accordance rent through the translating device is inwith theinvention. creased byone-half a milliampere the? tube Fig. Qshows amodiication thereof. V3 would be-givenfeight and one-'half volts f Fig, 3 shows'diagrammatical'ly Vthe uncmore negative bias due to the additional IR l Y drop through R2 andv by a reference to Fig.3, 85 Referring to Fig. 1 in the output 'circuit of Ifnd that; there Vvvill then be an IR -drop Vl` has been Ainserted the element VN, which of 135 voltsl of B1 across V3,Where -under the consists of a vacuum tube V3 the filament of previous condition with fourmilliampere's, which is heated by A3, resistance R2', conthere Wasbut sixty eight volts IR dropl across denser C2, and a resistance N1, which latter V3. It vis obviousthat the ampliiication of, 90

is characterized by having a very high'resist# Vl will be much less when the plate voltage ance until acertain voltage is-impre'ssed there impressed thereon is forty-five volts than on, atwhich time -it breaks down andv has. a wheny it kis one hundred and twelve volts, very -small resistance. Sucha resistance is When,- howe'ver, the'strength ofthe'incom-KV a neon lamp, a voltage regulator tube, a Geis` ing Ysignal increases beyondthe desired limit 95 ler tube, a small spark gap, The function ofv such as that caused by a crash of static the VN isto break-the circuit vwhen!surges of difference inv potential between thevpositive current above 'a'.predetermined liinitsucl'iv as terminal of :B1 andthe filamentotV 3 Will crashes of static yareim'pressed thereon, and thenbe overflLlO volts, as shown? in Fig, 3,

further to suppress blasting signals from fa Which willcauseresistance Nlto breakdown 100 and so greatly increase the negative bias on V3 as to virtually break the circuit thru the translating device, or load S. Thus the crash of static will not be recorded in the translating device.

F ig. 2 illustrates a modification in which two resistances are used, each of which has the characteristic of greatly decreasing its resistance as the voltage impressed thereon is increased. Under the ordinary operating condition N2 is inoperative, and non-conduc- 4 tive, the voltage impressed on N2 not being suflicient to break down the resistance thereof. If on the other hand the current in the circuit tends to increase so that the IR drop through resistance R4 and the translating device is greater than the break down voltage of N2, it will breakdown, become operative and conductive, and short circuit the translating device entirely.

At the time N2 breaks down, the voltage impressed on N3 is not sufficient to continue the conductive operation ofN3 due to the large current passing through R3 and the consequent large IR drop through R3, and consequently N3 will become inoperative and non-conductive. When the crash of static has passed the resistance of V4 is increased and voltage on N2 will not be suf'cient to continue its conductive operation, and N2 will become inoperative, consequently N3 will again break down and come into conductive operation.

R8 has the function of reducing the voltage impressed on N3 during the time that N2 is operative by means of by-passing a portion of the current past N3 and S, thereby producing a small IRV drop through R4.

C3 has the function of aiding in breaking down N3 and also decreasing the impedance of the circuit to audio frequency currents. The translating device circuit being completely broken during the period of time when the crash occurs, the crash will not be recorded therein. In one case, R3 and R4 were each ten thousand ohms. VThe conductive and nonconductive voltage of N3 was 110 volts, while the operative or conductive voltage of N2 was 125 volts and the inoperative or nonconductive voltage was 95 volts.

f When signals are passing through load S,

VN3 is operatively and conductively functioning and is broken down. When a crash of static occurs, N2 breaks down and functions to by-pass the-crash with respect to the load S,

N3 becoming temporarily inoperative, as above stated. A i

. While the device VN is shown as connected in the last stage of amplification, it is obvious thatit can be used even more eectively in a previous stage of amplification, and espe- Icially with a means of coupling wherein the current'through the coupling device is small, such as with resistance coupling, orv variable resistance coupling due to the fact that the current to be bypassed around the load in such circuits is less than the current in the output stage of the amplifying systems.

The invention has been disclosed in combination with particular typesV of circuits, and it is not considered that the invention is limited to the specific forms or means shown, the invention being described in the following claims.

It will be understood that where vacuum tube amplifier is referred to in the claims 1t will include within its meaning thermionic tjube amplifier or any equivalent tube ampli- 'IGI'.

What is claimed is:

1. In an electric circuit, a vacuum tube amplilier having an input and an output circuit, a source of signals for said input circuit, a

source of voltage for said output circuit, a

load in said output circuit, meansfor controlling the plate voltage impressed on said vacuum tube in accordance with the envelope of said signals, said means comprising a seoond vacuum tube having an anode, a cathode and a control electrode, said anode and said cathode being connected in said output circuit in series with said load, and an impedance connected between said cathode and said control` electrode Vand common to said output circuit. Y. n l

2. In an electric circuit a vacuum tube ampliiierhaving aninput and an'output circuit, a source of electrical variations for said input circuit, a source of voltagejfor said output circuit, a load in said output circuit, means for controlling the plate voltage impressed on said vacuum vtube in accordance with the envelope of said electrical varia- Y tions, said means comprising a second' vacuum tube having an anode, a cathode and a control electrode, said anode and said cathode being connected in series with said load in said output circuit, and a resistanceV shunted by a condenser connected between said cathode and said control electrode and common to said output circuit. Y

3. In an elect-ric circuit a vacuum tube amplifier having an input and-an output cirpredetermined value aroundsaid load, said lOll Said Control electrode. I

4. In an electrical circuit, a vacuum tube, having an input and an output circuit, a source of electrical variations for said input circuit, a source of voltage for said output circuit, a load in said output circuit, means for bypassing surges of current produced by said electrical variations above a predetermined value around saidv load, said means comprising a second vacuum tube having van anode, a cathode, and a control electrode, said anode and said cathode being connected inseries with said load in said output circuit,y a resistance shunted by a condenser connected between said cathode and said control electrode, and common to said output circuit, and a gas discharge device connected'across said output circuit to a terminal electrically remote from said control electrode. l

5. Ina stage of vacuum tube amplification, a vacuum tube having an input and an output circuit, a load in said output circuit, and means to render the receivingrgain of said stage appreciable less in response to large received current, than in response to currents corresponding to normal received signals,

said means comprising a second vacuum tube having an anode, a cathode and a control electrode, an impedance connecting said cathode to said control electrode, and common to said output circuit, 'and a normally non-conductive shunt bridged across said output circuit, and connected to said impedance Vat a point electrically remote from said control electrode.

6. In an electrical circuit a vacuum tube, f

having an input and an output circuit, a source of electrical variations for said input circuit, a source of current for said output circuit, a path for said current to flow in said output circuit, said path comprising a second vacuum tube having an anode, a cathode, and a control electrode, said anode and said cathode being connected in said path, an impedance connecting said cathode to said control electrode, said impedance Lbeing common to said output circuit, means for rendering said path appreciably less conductive for said variations above a predetermined value than for said variations below said predetermined value, said means comprising a normally non-conductive glowdischarge tube bridged across said output circuit connected to said impedance at a point electrically remote from said control electrode.

In testimony whereof I aiiX my signature.

OLIVER T. FRANCIS.` 

